1. Field of the Invention
The present invention relates generally to printing, and more particularly to a method for determining the ink drop velocity of a carrier-mounted printhead.
2. Description of the Related Art
Known printers include a printer, such as an inkjet printer, having a carrier-mounted printhead with print nozzles used to print ink on a print medium. The printhead carrier moves the printhead back and forth along a printhead-carrier-scanning axis at a gap above the print medium. Printing may be from left to right, from right to left or bidirectional (i.e., from left to right and from right to left). The print medium is advanced in a direction perpendicular to the printhead-carrier-scanning axis when the printhead has finished printing a scan line in one or more print passes. Printer also include all-in-one or multifunction machines adapted to function as at least two different devices, wherein a list of different devices includes a printer (such as an inkjet printer), a copier, a scanner (also called an optical scanner), a facsimile device, and a photo card reader.
The printhead is fired with enough energy to eject ink from the print nozzles at an ink drop velocity (defined to be the ink drop velocity relative to the printhead) having a direction along the ink ejection direction from the printhead to the print medium and having a magnitude typically in the range of 250 to 700 ips (inches per second) with 400 ips being an average number for a typical inkjet printer. From printhead lot to printhead lot, there are substantial variations in the amount of energy needed to attain this magnitude of the ink drop velocity. During printing, the ink drop velocity is assumed to have a particular magnitude. This assumed magnitude of the ink drop velocity is used to determine where the ink drop will land on the print medium if fired from a printhead having a gap between the printhead and the print medium and a known printhead carrier velocity.
This assumed magnitude of the ink drop velocity is often wrong. The effect is that ink drops do not land exactly where intended. It does not matter if the actual magnitude of the velocity is greater or less than the assumed magnitude; the net effect is still the same. Known printhead alignment procedures can compensate for some of this variation, but if the actual magnitude of the ink drop velocity could be determined, print quality could be enhanced. Known techniques for determining the ink drop velocity include measuring the time it takes for the ink drop to pass between two optical drop sensors spaced a distance apart above the print medium. What is needed is an improved method for determining the ink drop velocity of a carrier-mounted printhead.